The present invention relates to a vehicle engine intake muffler. More specifically, the present invention relates to a vehicle engine intake muffler for quieting the intake system of an automobile engine.
An automobile engine takes in air, mixes it with fuel, and then burns the air/fuel mixture. The larger the output of the engine, the greater the amount of air which must be taken in. As air is taken into the engine, the air produces an intake sound. This sound is naturally louder as the amount of air taken in increases. At times, the intake sound is loud enough to be heard inside the vehicle, making the ride less pleasant. The intake sound is reduced or eliminated by attaching a resonator to a part of the intake pipe path. The intake sounds vary in frequency, depending on the intake path and engine shape and volume. A resonator, however, is unable to reduce all frequencies of intake sound. There are some sounds that a resonator can effectively reduce or eliminate. On the other hand, there are some intake sounds on which a resonator has little effect.
Since today's automobiles finely control their engine to match many conditions, the frequencies of intake sound are not monotonic but highly varied. This is dealt with by attaching multiple resonators for different intake frequencies to a single intake pipe path. Today's automobiles, however, have a large number of accessories to meet various requirements, such as better engine efficiency, cleaner exhaust gas, and improved brake performance. These accessories reduce the space available in the engine compartment, imposing many constraints on where resonators can be located.
Some of the parts of the intake pipe path are relatively bulky. By housing these bulky parts inside the front-wheel fenders, which usually is dead space, space in the interior of the engine compartment is freed to readily accommodate other equipment as well as the engine. If parts of the intake system are put inside the fenders however, when the vehicle runs down a flooded street, there is danger that splashed water will get sucked into the intake pipe path. Thus, it is necessary to have some means to eliminate water from getting inside the intake pipe path.
Referring to FIGS. 9 and 10, a conventional method of arranging part of the intake pipe path inside the fender is illustrated. An automobile 1 has a fender 3 above front wheel 2. A bumper 4 is located to the front of fender 3. A headlamp 5 is at the front of fender 3. An air suction pipe 6, whose midsection is bent in roughly a U shape, is inside fender 3. An intake port 6a faces forward at the tip of air suction pipe 6. Since intake port 6a is the source of the intake noise, air suction pipe 6 has a structure in which the part that faces toward the rear of the chassis is bent in a U shape toward the front, away from the driver's seat.
The base end of air suction pipe 6 is joined through an air suction hose 7 to the intake side of an air cleaner 8. A connection opening 9a of a first resonator 9 connects to a part where air suction hose 7 branches. First resonator 9, having a large volume with respect to the other resonators, is positioned inside bumper 4.
The outlet side of air cleaner 8 joins to the engine intake manifold through an air cleaner outlet hose 10 and a throttle body (not shown). Between part of air cleaner 8 and the midsection of air cleaner outlet hose 10, a second resonator 11, having the shape of a crooked pipe, is connected by clip 12.
In the convention intake pipe path, air taken in from intake port 6a of air suction pipe 6 goes through air suction hose 7 to enter air cleaner 8, where dust is removed. The air then enters the engine intake manifold from air cleaner outlet hose 10 via the throttle body. In this process, a pulsing sound is produced by the intake pulsing as the engine intake valve opens and closes. This pulsing sound is a relatively low-frequency sound whose fundamental period is the ignition period, but it is effectively attenuated by first and second resonators 9 and 11.
Of the two resonators 9 and 11, first resonator 9, on the intake side of air cleaner 8, does not have any strict requirement for airtightness of its junction part. Thus, first resonator 9 is attached by being fitted into air suction hose 7. Second resonator 11, on the outlet side of air cleaner 8, has a greater need for airtightness. Thus, second resonator 11 is firmly held in place by clip 12. Because first resonator 9 is in a relatively low position, it tends to collect water that intrudes from the various parts of the intake pipe path. When water pools in first resonator 9, the frequency of the suction sound changes, and the designed effect is not obtained. To avoid this, a small hole 9a drains water from first resonator 9.
First and second resonators 9 and 11 are used in the above-described structure. As stated above, however, modern engines produce intake sounds of multiple frequencies. Since automobile users have an increasingly strict desire to muffle these sounds, it is desirable to have a greater number of resonators. However, it has been difficult to put on a third resonator simply, easily, and cheaply in the limited space that is available.
A structure of a muffler that reduces the noise in multiple different frequency ranges is disclosed in Japanese unexamined patent application publication H9-317581 [1997]. The invention of this publication has first and second chambers arranged parallel to each other on opposite sides of the duct pipe. Air is introduced, and noise in different frequency ranges is reduced by these first and second chambers. The difference between the structure of JP H9-317581 and the conventional structure described above is that the first and second chambers are integrally joined to the two ends of the duct pipe. However, since there are still only two chambers, the sound-deadening effect is the same as in the above-described conventional product.
A structure in which the length of the path to which the resonator is connected is varied is disclosed in Japanese unexamined patent application publication H7-103094 [1995]. The invention of this publication has, in the resonator-side pipe path, a path length setting wall part that sets the length of the path. However, this structure has only one resonator structure Thus, its content is different from the present invention, which seeks to increase the number of resonators in a product that has multiple resonators.